Ecological functions of an impounded marsh and three natural estuarine marshes along Woodbridge River,NY/NJ Harbor

An impounded estuarine marsh scheduled for restoration in 2003 and three nearby unimpounded marshes (Spartina alterniflora, S. patens/Iva frutescens, and Phragmites australis) in highly urbanized NY/NJ Harbor were studied to assess the impact of impoundment on marsh structure and function and to identify trajectories of ecosystem change following removal of the levee. Aboveground biomass was greater in the Phragmites and S. alterniflora marshes (706–809 g/m²) as compared to the S. patens/I. frutescens and impounded marshes (378–588 g/m²). Macro-organic matter (0–30 cm) was similar across all marshes (7452–9212 g/m²). The S. patens/Iva frutescens marsh had the lowest aboveground biomass, but contained more plant species (2.8 species/0.25 m²) and greater species diversity (H = 1.33) than the other marshes (1.3–2.0 species/0.25 m², H = 0.16–0.78). Rates of sediment and nutrient accumulation were lower in the impounded marsh (335 g sediment/m²/yr, 97 g C/m²/yr, 6.5 g N/m²/yr, and 0.9 g P/m²/yr) than in the reference marshes (422–1515 g sediment/m²/yr; 111–160 g C/m²/yr; 7–10 g N/m²/yr; 1.6–2.8 g P/m²/yr). Our results indicate that the impounded marsh does not contain the high species diversity of the high marsh, nor does it provide the same level of functions as naturally inundated marshes. Reintroduction of tidal inundation to the impounded marsh will enhance water quality benefits and favor development of S. alterniflora salt marsh community structure.